Composition for hologram-recording material, hologram-recording medium, and process for producing the same

ABSTRACT

An object of the present invention is to provide a hologram recording material composition which is excellent in transparency and diffraction efficiency. The hologram recording material composition comprises a thermoplastic resin (A) which is soluble in a solvent, a radical polymerizable compound (B) which is solid at an ordinary temperature and at ordinary pressure and has the 9,9-diarylfluorene skeleton and at least one radical polymerizable unsaturated double bond, a plasticizer (C) and a photopolymerization initiator (D). A weight percentage ratio of the thermoplastic resin (A), the radical polymerizable compound (B) and the plasticizer (C), (A):(B):(C) is 10 to 80:10 to 80:10 to 80. A refractive index of the radical polymerizable compound (B) is larger than a weighted mean of that of the thermoplastic resin (A) and that of the plasticizer (C).

TECHNICAL FIELD

[0001] The present invention relates to a novel volume phase-typehologram recording material composition to be used for recordingintensity distribution of light and shade of a light interferencepattern as a change in refractive index, and particularly a hologramrecording material composition for producing a recording medium which isexcellent in transparency and diffraction efficiency, which arefundamental characteristics required for a hologram, and it also relatesto a hologram recording medium obtained therefrom and a process forproducing the same.

BACKGROUND ART

[0002] A hologram is a record of an interference fringe of coherentlaser light on a photosensitive material, and is used in various field,such as an optical device, a three-dimensional display, interferometryand processing of an image and information, owing to themulti-functionality thereof.

[0003] As a representative example of the conventional hologramrecording material composition, a gelatin dichromate photosensitivematerial and a breached silver salt photosensitive material (described,for example, in Display Holography Handbook, p. 66 to 67 (Gyoin Shokan,1985) and Optical Engineering Handbook, p. 351 to 353 (Asakura Shoten,1986)).

[0004] However, although gelatin dichromate has a high diffractionefficiency, and a silver salt photosensitive material has a highsensitivity, these materials require a complicated process on productionof a hologram, and particularly they have a problem in that they requirea wet development process.

[0005] As a photosensitive material to eliminate the problem, a hologramrecording material composition containing a photo-polymerizable monomeris proposed. In this material, a photo-polymerizable monomer ispolymerized in a portion having a large light amount in the interferencefringe to cause a refractive index modulation in that portion, and thusa hologram is recorded. Examples thereof include a photo-polymerizationtype recording material mainly comprising cyclohexyl methacrylate andN-vinylcarbazole as photopolymerizable monomers; and aphoto-polymerization initiator, and a photo-polymerization typerecording material mainly comprising butyl methacrylate and ethyleneglycol dimethacrylate as photopolymerizable monomers, and1-phenylnaphthalene as an inactive component not participating in thepolymerization; and a photo-polymerization initiator (as described inAppl. Opt., vol. 15, p. 534 (1976), U.S. Pat. No. 3,993,485 and thelike).

[0006] However, because these materials are in a liquid state, thecomposition flows between two surface materials on recording a hologramto prevent recording in good conditions. Furthermore, an unreactedmonomer remains after recording the hologram in a portion of a smalllight amount, and therefore the record is necessarily stabilized byconducting an exposure treatment on the whole surface.

[0007] In order to solve the above-mentioned problems of the prior arts,it is proposed that a polymer which does not participate inphotoreaction is used as a binder in order to inhibit fluidization ofcompositions, and the polymer is used in combination with aphotopolymerizable monomer which is liquid at an ordinary temperature(U.S. Pat. No. 3,658,526). These compositions do not require treatmentsuch as heating before and after recording holograms and can prepare theholograms only by simple dry treatment. However, this technique isinferior to the above-mentioned gelatin dichromate and silver saltphotosensitive material in diffraction efficiency, which representsessential performance of the holograms.

[0008] As improvement of the above-mentioned prior art, compositionsconsisting essentially of a binder polymer, a liquid photopolymerizablemonomer having a high refractive index, a plasticizer and aphotopolymerization initiator, the photopolymerizable monomer containingan atom which contributes to the high refractive index such as chlorineor bromine in order to improve refractive modulation are proposed (U.S.Pat. Nos. 4,942,102 and 4,942,112 and the like). In the case of thesecompositions, compatibility with the plasticizer was often poor, andthere were problems such as insufficient solubility of the compositions,haze and the like. Since recorded holograms had insufficient diffractionefficiency, it was necessary to perform heat treatment or the like afterrecording again to amplify the diffraction efficiency, andpost-treatment was still troublesome.

[0009] As improvement of the above-mentioned prior art, compositionscomprising a polymeric binder, a radical polymerizable compound having a9,9-diarylfluorene skeleton and being liquid at an ordinary temperature,a plasticizer and a photopolymerization initiator are proposed (JapaneseLaid-open Patent Publication No. 301322/1994). The publication disclosesthat since the radical polymerizable compound does not contain chlorine,bromine or the like and has the 9,9-diarylfluorene skeleton in order toincrease a refractive index, the compound is compatible with componentssuch as the binder polymer.

[0010] However, there existed the problem that since the compound isliquid at an ordinary temperature and has a lower refractive index thana monomer which is solid at an ordinary temperature, sufficientdiffraction efficiency is not obtained in holograms after recording.Accordingly, a combination of the monomer having a higher refractiveindex and being solid at an ordinary temperature with the polymericbinder was desired. However, there existed the problem that when themonomer which is solid at an ordinary temperature is used, thephotosensitive material causes haze, and sufficient optical transmissionis not obtained.

DISCLOSURE OF THE INVENTION

[0011] An object of the present invention is to provide a hologramrecording material composition comprising a radical polymerizablecompound being solid at an ordinary temperature and having a9,9-diarylfluorene skeleton, a polymeric binder, a plasticizer and aphotopolymerization initiator, the composition being excellent intransparency and diffraction efficiency, which are characteristicsrequired for a hologram.

[0012] As a result of earnest investigations to attain the objectdescribed above by the inventors, a novel hologram recording materialcomposition has been developed to complete the invention.

[0013] Namely, the present invention relates to a volume phase-typehologram recording material composition to be used for recordingintensity distribution of light and shade of an interference patternobtained by making light interfere as a change in refractive index,characterized in that the composition comprises a thermoplastic resin(A) which is soluble in an organic solvent, a radical polymerizablecompound (B) which is solid at an ordinary temperature and at ordinarypressure and has the 9,9-diarylfluorene skeleton and at least oneradical polymerizable unsaturated double bond, a plasticizer (C) and aphotopolymerization initiator (D), a weight percentage ratio of thethermoplastic resin (A), the radical polymerizable compound (B) and theplasticizer (C), (A):(B):(C) is 10 to 80:10 to 80:10 to 80, and arefractive index of the radical polymerizable compound (B) is largerthan a weighted mean of that of the thermoplastic resin (A) and that ofthe plasticizer (C).

[0014] Weight-average molecular weight of the thermoplastic resin (A) ispreferably 10,000 to 5,000,000 in order to obtain good processingcharacteristics.

[0015] The thermoplastic resins (A) to be used in the present inventioncan be any resins which are compatible with the radical polymerizablecompound (B) and the plasticizer (C) and can be dissolved in an organicsolvent completely without an insoluble matter. A typical thermoplasticresin is selected from the group consisting of homopolymers of a monomerhaving an ethylenic unsaturated double bond, copolymers of the monomerand a copolymerizable monomer which can be copolymerized with themonomer, condensation polymerization products of a diphenol compound anda dicarboxylic acid compound, polymers having a carbonate group in amolecule thereof, polymers having an —SO₂— group in a molecule thereof,cellulose derivatives and combinations thereof.

[0016] Specific examples of thermoplastic resins (A) are polyvinylacetate, polyvinyl butyrate, polyvinyl formal, polyvinyl carbazole,polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethylmethacrylate, polyethyl acrylate, polybutyl acrylate,polymethacrylonitrile, polyethyl methacrylate, polybutyl methacrylate,polyacrylonitrile, poly-1,2-dichloroethylene, ethylene-vinyl acetatecopolymers, syndiotactic polymethyl methacrylate, poly-α-vinylnaphthalate, polycarbonate, cellulose acetate, cellulose triacetate,cellulose acetate butyrate, polystyrene, poly-α-methylstyrene,poly-o-methylstyrene, poly-p-methylstyrene, poly-p-phenylstyrene,poly-2,5-dichlorostyrene, poly-p-chlorostyrene, poly-2,5-dichlorostyrene, polyarylate, polysulfone, polyethersulfone,styrene-acrylonitrile copolymers, styrene-divinylbenzene copolymers,styrene-butadiene copolymers, styrene-maleic anhydride copolymers, ABSresins, polyethylene, polyvinyl chloride, polypropylene, polyethyleneterephthalate, polyvinyl pyrrolidone, polyvinylidene chloride,hydrogenated styrene-butadiene-styrene copolymers, transparentpolyurethane, polytetrafluoroethylene, polyvinylidene fluoride andcopolymers of cyclic aliphatic(meth)acrylate and methyl(meth)acrylate.

[0017] The above-mentioned examples of thermoplastic resins (A) can beused solely or in combination.

[0018] The thermoplastic resins (A) preferably have a glass transitiontemperature (Tg) of 100° C. or higher.

[0019] Various thermoplastic resins (A) can be selected depending onuse, application and the like of holograms. Polyvinyl acetate, polyvinylbutyrate, cellulose acetate butyrate, the ethylene-vinyl acetatecopolymers, polymethyl methacrylate, polystyrene, polyvinyl formal andthe like are preferably used in order to obtain a good film formingproperty and good optical quality such as diffraction efficiency.

[0020] The copolymers of cyclic aliphatic(meth)acrylate andmethyl(meth)acrylate are preferable in order to obtain better heatresistance, film forming property and optical quality such asdiffraction efficiency.

[0021] A copolymerization composition ratio of cyclicaliphatic(meth)acrylate to methyl(meth)acrylate constituting thecopolymers of cyclic aliphatic(meth)acrylate and methyl(meth)acrylate tobe used in the present invention is preferably 5 to 95:95 to 5, morepreferably 10 to 90:90 to 10 expressed in a molar ratio (the ester: theacrylate).

[0022] Cyclic aliphatic(meth)acrylate constituting the copolymers ofcyclic aliphatic(meth)acrylate and methyl(meth)acrylate can berepresented by the following general formula [I],

[0023] wherein R¹ and R², the same or different, are hydrogen or loweralkyl, “1” is an integer of 0 to 6, “m” is an integer of 2 to 6, “n” isan integer of 1 to 5 which is smaller than “m”. Any hydrogen atom(s) inalkylene chains (CH₂)₁, (CH₂)_(m) and (CH₂)_(n) can be substituted bylower alkyl. Two hydrogen atoms linked to different carbon atoms in thealkylene chain (CH₂)_(m) can be substituted by both terminals of anotheralkylene chain having one to eight carbon atoms to form anothercycloalkane ring. Any hydrogen atom(s) in this cycloalkane ring can befurther substituted by lower alkyl. One of carbon atoms in the alkylenechain (CH₂)_(n) has hydroxyl, to which (meth)acrylic acid is linked toform an ester linkage, and the broken line ( - - - ) is the esterlinkage thus formed.

[0024] A cyclic aliphatic moiety of cyclic aliphatic(meth)acrylateconstituting the copolymers of cyclic aliphatic(meth)acrylate andmethyl(meth)acrylate can have a bornyl skeleton, an isobornyl skeletonor a norbornyl skeleton.

[0025] Examples of cyclic aliphatic(meth)acrylate constituting thecopolymers of cyclic aliphatic(meth)acrylate and methyl(meth)acrylateare bornyl(meth)acrylate, isobornyl(meth)acrylate andnorbornyl(meth)acrylate.

[0026] Cyclic aliphatic(meth)acrylate can be one kind or two or morekinds. In the latter case, the copolymer is a terpolymer or higher oftwo or more kinds of cyclic aliphatic(meth)acrylate andmethyl(meth)acrylate.

[0027] Glass transition temperatures of the copolymers of cyclicaliphatic(meth)acrylate and methyl(meth)acrylate are preferably 130° C.or higher.

[0028] The copolymers of cyclic aliphatic(meth)acrylate andmethyl(meth)acrylate can be used solely or in combination.

[0029] The radical polymerizable compounds (B) to be used in the presentinvention have the 9,9-diarylfluorene skeleton and at least one radicalpolymerizable unsaturated double bond and are solid at an ordinarytemperature and at ordinary pressure. The solid is a state having anendothermic peak at room temperature or higher, which is due to phasetransition from a solid to a liquid in differential thermal analysis.

[0030] The radical polymerizable compounds (B) can be represented by thefollowing general formula [II],

[0031] wherein R³ and R⁴, the same or different, are monovalent organicgroups at least one of which has (meth)acryloyl or (meth)acryloyloxy atits terminal, M₁ and M², the same or different, are divalent organicgroups represented by —(OR)_(n)— (wherein R is lower alkylene which canhave hydroxyl, and “n” is an integer of 0 to 2) or single bonds, and X¹and X², the same or different, are hydrogen or lower alkyl.

[0032] The organic group having no (meth)acryloyl or (meth)acryloyloxyin R³ and R⁴ can be lower alkyl having one to three carbon atoms.

[0033] In —(OR)_(n)— of M¹ and M², a carbon number of the lower alkyleneR is preferably one to three, more preferably one or two. When “n” istwo, two Rs can be the same or different. Examples of OR areoxymethylene, oxyethylene, oxypropylene, oxybutylene and the like.Examples of (OR)₂ are dimethoxy, diethoxy and propoxyethoxy. When thelower alkylene R has hydroxyl, the hydroxyl can exist at any positionsof the alkylene, and an example of the alkylene having hydroxyl is(2-hydroxy)propylene.

[0034] The organic groups X¹ and X² can be alkyl having one to fivecarbon atoms such as methyl, ethyl or propyl.

[0035] The radical polymerizable compounds (B) are exemplifiedhereinafter;

[0036] 9,9-bis(4-(meth)acryloyloxyphenyl)fluorene,

[0037] 9,9-bis(4-(meth)acryloyloxymethoxyphenyl)fluorene,

[0038] 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene,

[0039] 9,9-bis[4-(meth)acryloyloxy-3-methylphenyl]fluorene,

[0040] 9,9-bis[4-(meth)acryloyloxymethoxy-3-methylphenyl]fluorene,

[0041] 9,9-bis[4-(2-(meth)acryloyloxyethoxy)-3-methylphenyl]fluorene,

[0042] 9,9-bis(4-(meth)acryloyloxy-3-ethylphenyl)fluorene,

[0043] 9,9-bis(4-(meth)acryloyloxymethoxy-3-ethylphenyl)fluorene,

[0044] 9,9-bis[4-(2-(meth)acryloyloxyethoxy)-3-ethylphenyl]fluorene,

[0045] 9,9-bis[4-(2-(meth)acryloyloxypropoxy)-3-ethylphenyl]fluorene,

[0046] 9,9-bis[4-(3-(meth)acryloyloxy-2-hydroxy)propoxyphenyl]fluorene,

[0047]9,9-bis[4-(3-(meth)acryloyloxy-2-hydroxy)propoxy-3-methylphenyl]fluoreneand9,9-bis{4-[2-(3-acryloyloxy-2-hydroxy-propoxy)-ethoxy]phenyl}fluorene.

[0048] The radical polymerizable compounds (B) can be oligomers such asdimers or trimers of the above-mentioned compound.

[0049] The above-mentioned exemplified compounds can be used solely orin combination.

[0050] It is preferable that both the organic groups R³ and R⁴ areacryloyl and acryloyloxy, and “n” is an integer of zero to two, thecarbon number of the lower alkylene R is one or two in —(OR)_(n)— of M¹and M², and X₁ and X₂ are hydrogen in order to obtain a good filmforming property and good optical quality such as diffractionefficiency.

[0051] Examples of preferred compounds satisfying the above-mentionedconditions are 9,9-bis[4-(3-acryloyloxy-2-hydroxy)propoxyphenyl]fluorene(produced by Nippon Steel Chemical Co., Ltd., “acrylic acid adduct of9,9-bis(4-hydroxyphenyl)fluorene glycidyl ether, ASF400”),9,9-bis(4-methacryloyloxyphenyl)fluorene (produced by Nippon SteelChemical Co., Ltd., “bisphenolfluorene dimethacrylate”),9,9-bis(4-acryloyloxyphenyl)fluorene,9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene (produced by Osaka GasCo., Ltd., “bisphenoxyethanolfluorene diacrylate, BPEF-A”),9,9-bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene (produced by OsakaGas Co., Ltd., “bisphenoxyethanolfluorene dimethacrylate, BPEF-MA”),9,9-bis[4-[2-(3-acryloyloxy-2-hydroxy-propoxy)-ethoxy]phenyl]fluorene(produced by Osaka Gas Co., Ltd., “bisphenoxyethanolfluorenediepoxyacrylate, BPEF-GA”) and9,9-bis[4-(3-acryloyloxy-2-hydroxy)propoxy-3-methylphenyl]fluorene(produced by Osaka Gas Co., Ltd., “biscresolfluorene diepoxyacrylate,BCF-GA”).

[0052] Examples of more preferred compounds are

[0053] 9,9-bis[4-(3-acryloyloxy-2-hydroxy)propoxyphenyl]fluorene,

[0054] 9,9-bis(4-methacryloyloxyphenyl)fluorene,

[0055] 9,9-bis(4-acryloyloxyphenyl)fluorene,

[0056] 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene and

[0057] 9,9-bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene.

[0058] The plasticizers (C) to be used in the present invention arecompounds which are unreactive with the thermoplastic resins (A) and theradical polymerizable compounds (B). Examples of plasticizers (C) areinactive compounds such as phthalates represented by dimethyl phthalate,diethyl phthalate and dioctyl phthalate; aliphatic dibasic acid estersrepresented by dimethyl adipate, dibutyl adipate, dimethyl sebacate,diethyl sebacate, dibutyl sebacate and diethyl succinate;orthophosphates represented by trimethyl phosphate, triethyl phosphate,triphenyl phosphate and tricresyl phosphate; acetates represented byglyceryl triacetate and 2-ethylhexyl acetate; and phosphites representedby triphenyl phosphite and dibutylhydrodiene phosphite.

[0059] Alkylene glycol alkyl ethers represented by the following generalformula [III] can also be used,

[0060] wherein R¹¹ and R¹², the same or different, are alkyl having oneto five carbon atoms, hydroxyl or acetyl, and “n” is an integer of 1 to5.

[0061] Typical examples of alkylene glycol alkyl ethers are ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycoldipropyl ether, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol monopropyl ether, diethylene glycoldimethyl ether, diethylene glycol diethyl ether, diethylene glycoldipropyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monopropyl ether, triethylene glycoldimethyl ether, triethylene glycol diethyl ether, triethylene glycoldipropyl ether, triethylene glycol monomethyl ether, triethylene glycolmonoethyl ether, triethylene glycol monopropyl ether, cellosolve acetateethylene glycol diacetyl ether, ethylene glycol monoacetyl ether,diethylene glycol diacetyl ether, diethylene glycol monoacetyl ether,triethylene glycol diacetyl ether and triethylene glycol monoacetylether.

[0062] It is also possible to use polyethylene glycol having aweight-average molecular weight of 10,000 or lower or silicone oil.

[0063] It is preferable to select a plasticizer (C) having a refractiveindex being much smaller than those of the thermoplastic resins (A).

[0064] The above-mentioned exemplified compounds can be used solely orin combination.

[0065] When the weight percentage ratio of the thermoplastic resin (A),the radical polymerizable compound (B) and the plasticizer (C),(A):(B):(C) is 10 to 80:10 to 80:10 to 80, the hologram recordingmaterial compositions according to the present invention are excellentin transparency and diffraction efficiency. When the ratio of (A), (B)and (C) does not fall in this range, holograms cannot be recorded, orthe diffraction efficiency falls. The weight percentage ratio,(A):(B):(C) is preferably 20 to 70:10 to 60:20 to 70, more preferably 30to 60:15 to 45:25 to 55.

[0066] These components are selected in the hologram recording materialcompositions according to the present invention so that the refractiveindex of the radical polymerizable compound (B) is as larger aspossible, preferably larger by 0.005 or more than the weighted mean ofthat of the thermoplastic resin (A) and that of the plasticizer (C).When the refractive index of the radical polymerizable compound (B) issmaller than the weighted mean of that of the thermoplastic resin (A)and that of the plasticizer (C), the holograms sometimes cannot berecorded, or the diffraction efficiency falls.

[0067] As the photo-polymerization initiator (D) used in the presentinvention, there can suitably be used those forming a radical byabsorbing laser light, such as He—Ne laser (wavelength: 633 nm), Arlaser (wavelength: 515 and 488 nm), YAG laser (wavelength: 532 nm) andHe—Cd laser (wavelength: 442 nm) as light sources. As thephoto-polymerization initiator, for example, there can preferably beused a carbonyl compound, an amine compound, an arylaminoacetic acidcompound, an organotin compound, an alkylarylborate, an onium salt, aniron arene complex, a trihalogenomethyl-substituted triazine compound,an organic peroxide, a bisimidazole derivative, a titanocene compoundand combinations of these initiators and a photosensitizing dye.

[0068] Examples of carbonyl compounds include benzil, benzoin ethylether, benzophenone and diethoxyacetophenone.

[0069] Examples of amine compounds are triethanolamine,triisopropanolamine and 2-dimethylaminobenzoic acid.

[0070] An example of arylaminoacetic acid compounds is N-phenylglycine.

[0071] An example of organotin compounds is tributylbenzyltin.

[0072] Examples of alkylarylborates are tetrabutylammoniumtriphenylbutylborate and triphenyl-n-butylborate.

[0073] An example of onium salts is a diphenyliodonium salt.

[0074] An example of iron arene complexes isη⁵-cyclopentadienyl-η⁶-cumenyl-iron (1+)-hexafluorophosphate (1−).

[0075] An example of trihalogenomethyl-substituted triazine compounds istris(trichloromethyl)triazine.

[0076] An example of organic peroxides is3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone.

[0077] Examples of bisimidazole derivatives are2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole andbis(2,4,5-triphenyl)imidazolyl.

[0078] An example of titanocene compounds isbis(η⁵-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1-H-pyrrol-1yl)phenyl)titanium.

[0079] These can be used solely or in combination.

[0080] As the photosensitizing dye, Michler's ketone, Acridine Yellow,merocyanine, methylene blue, camphorquinone, Eosin and decarboxylatedrose bengal are preferably used. Any photosensitizing dye can be used asfar as it exhibits absorption in the visible region, and in addition tothe above, a cyanine derivative, a merocyanine derivative, aphthalocyanine derivative, a xanthene derivative, a thioxanthenederivative, an acridine derivative, a porphyrin derivative, a coumarinderivative, a basestyryl derivative, a ketocoumarin derivative, aquinolone derivative, a stilbene derivative, an oxazine derivative and athiazine dye can be used. Furthermore, photo-sensitizing dyes describedin Dye Handbook, edited by S. Ohgawara, et al. (Kodansha, 1986),Chemistry of Functional Dyes, edited by S. Ohgawara, et al. (CMC, 1983),and Special Functional Materials, edited by C. Ikemori, et al. (CMC,1986) can be used. These can be used singly or in combination of two ormore.

[0081] Examples of coumarin derivatives are

[0082] 3-(2-benzothiazolyl)-7-(diethylamino)coumarin,

[0083] 3-(2-benzothiazolyl)-7-(dibutylamino)coumarin,

[0084] 3-(2-benzothiazolyl)-7-(dioctylamino)coumarin and

[0085] 3-(2-benzimidazolyl)-7-(diethylamino)coumarin.

[0086] Examples of ketocoumarin derivatives are

[0087] 3,3′-carbonylbis(7-diethylaminocoumarin),

[0088]3,3′-carbonylbis-7-diethylaminocoumarin-7′-bis(butoxyethyl)-aminocoumarinand 3,3′-carbonylbis(7-dibutylaminocoumarin).

[0089] Examples of basestyryl derivatives are

[0090] 2-[p-(dimethylamino)styryl]benzothiazole,

[0091] 2-[p-(dimethylamino)styryl]naphtho[1,2- d]thiazole and

[0092] 2-[(m-hydroxy-p-methoxy)styryl]benzothiazole.

[0093] Examples of merocyanine derivatives are3-ethyl-5-[(3-ethyl-2(3H)-benzothiazolylidene)ethylidene]-2-thioxo-4-oxazolidinoneand5-[(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene]-3-ethyl-2-thioxo-4-oxazolidinone.

[0094] Specific examples of combinations of the organic peroxide and thephotosensitizing dye include combinations of3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone and NKX653,NKX3883, NKX1880, NKX1595, NKX1695, NK4256, NK1886, NK1473, NK1474,NK4795, NK4276, NK4278, NK91, NK1046, NK1237, NK1420, NK1538, NK3590 andthe like, which are photosensitizing dyes produced by NipponPhotosensitizing Dye Laboratory Co., Ltd.

[0095] Combinations of “B-CIM” produced by Hodogaya Chemical Co., Ltd.as a bisimidazole derivative, chain-transfer agents such as2-mercaptobenzoxazole and 2-mercaptobenzothiazole and theabove-mentioned photosensitizing dyes can also be suitably used.

[0096] Specific examples of combinations of the carbonyl compound andthe photosensitizing dye include benzil-Michler's ketone, andbenzil-Acridine Yellow. As the photosensitizing dye used in combinationwith the amine compound, decarboxylated rose bengal is preferred. As thephotosensitizing dye used in combination with the borate compound, acyanine-based dye, such as a cyanine, an isocyanine and a pseudocyanine.

[0097] The amount of the photo-polymerization initiator (D) added to thecomposition of the invention is generally about from 0.1 to 15% byweight, and preferably about from 0.3 to 10% by weight, based on 100parts by weight of the total amount of the thermoplastic resin (A), theradical polymerizable compound (B) and the plasticizer (C) in the casewhere the carbonyl compound is used.

[0098] The hologram recording material composition of the invention cancontain additives, such as a thickener, a compatibility adjusting agent,a heat polymerization inhibitor and a chain transfer agent, and asolvent, if necessary.

[0099] Inorganic fine particles and organic fine particles can be usedas the thickener. Examples of inorganic fine particles include silicagel fine particles “Daiso gel SP series” produced by Daiso Co., Ltd.,“Silicia” and “Fuji silica gel” produced by Fuji Silicia Chemical Co.,Ltd., “Carplex” produced by Shionogi & Co., Ltd., “Aerosil” produced byNippon Aerosil Co., Ltd., “Reorosil”, “Tokusil” and “Finesil” producedby Tokuyama Co., Ltd. and the like. Examples of organic fine particlesinclude a diallyl phthalate-based polymer which can be obtained bymethods described in JP-A 10-72510 and JP-A 10-310684; and “PB 200series” produced by Kao Corporation, “Bell Pearl series” produced byKanebo Ltd., “Techpolymer series” produced by Sekisui Plastics Co.,Ltd., “Micropearl series” produced by Sekisui Fine Chemical Co., Ltd.,and “MR series” and “MP series” both produced by Soken Chemical &Engineering Co., Ltd., which are described in “Most advanced technologyof microfine particles”, edited by S. Muroi (CMC, 1991). A particlediameter of these fine particles can be smaller than film thickness ofthe hologram and is preferably 0.1 to 20 nm. The amount of theplasticizer added is preferably about from 0.5 to 30 parts by weight per100 parts by weight of the total amount of the thermoplastic resin (A),the radical polymerizable compound (B) and the plasticizer (C).

[0100] The organic solvent is effective to improve the film formingproperty, as well as the viscosity adjustment and the compatibilityadjustment. For example, acetone, xylene, toluene, methyl ethyl ketone,tetrahydrofuran, benzene, methylene chloride, dichloromethane,chloroform, methanol and the like are usually used. However, watercannot be used since water inhibits the viscosity adjustment, thecompatibility adjustment, the film forming property and the like. Watercannot be used as a medium even in the form of emulsion. The amount ofthe solvent used is about from 0.5 to 1,000 parts by weight per 100parts by weight of the total amount of the thermoplastic resin (A), theradical polymerizable compound (B) and the plasticizer (C).

[0101] Examples of heat polymerization inhibitors include hydroquinone,p-methoxyphenol, tert-butylcatechol, naphthylamine,diphenylpicrylhydrazine, diphenylamine and the like, which work toconsuming the forming radicals.

[0102] Examples of the chain transfer agent include an α-methylstyrenedimer, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, tert-butylalcohol, n-butanol, isobutanol, isopropylbenzene, ethylbenzene,chloroform, methyl ethyl ketone, propylene, vinyl chloride and the like.

[0103] In order to prepare the hologram recording material composition,for example, the thermoplastic resin (A), the radical polymerizablecompound (B), the plasticizer (C) and the photo-polymerization initiator(D), as well as the optional components described above, the additivesand the solvent are placed in a vessel resistant to an organic solvent,such as a glass beaker, and the whole content is stirred. In this case,in order to accelerate dissolution of solid components, the compositioncan be heated to a range in which denaturation of the composition doesnot occur, such as to a temperature of about from 40 to 90° C.

[0104] In order to produce a hologram recording medium by using thehologram recording material composition of the invention, the recordingmaterial composition is coated on one surface of a substrate to obtain arecording medium having a two-layer structure consisting of the coatedfilm thus formed, i.e., a recording layer (photosensitive film forrecording), and the substrate. A three-layer structure is obtained, ifnecessary, by placing a protective material in the form of a film, asheet or a plate to cover the recording layer formed on the substrate.In the process for preparing the recording layer, an organic solvent ispreferably used. In this case, the thermoplastic resin (A), the radicalpolymerizable compound (B), the plasticizer (C) and thephoto-polymerization initiator (D) are dissolved in a solvent, and asolution thus obtained is coated on a substrate. Thereafter, the solventis vaporized to obtain a recording layer. In the case where a protectivematerial is placed to cover the recording layer, it is preferred thatthe solvent is removed by air drying, vaporization under reducedpressure or heating before placing the protective material. Thesubstrate is made of an optically transparent material, such as a glassplate and a plastic plate, such as a polyethylene terephthalate(hereinafter abbreviated as PET) plate, a polycarbonate plate and apolymethyl methacrylate plate or a film. The thickness of the substrateis preferably from 0.02 to 10 mm. The protective material is also madeof an optically transparent material as similar to the substrate. Thesubstrate does not necessarily have to be flat, but can be bent orcurved and can have an uneven structure on the surface thereof. Thethickness of the protective material is preferably from 0.02 to 10 mm.Examples of the coating method include a gravure coating method, a rollcoating method and a bar coating method. The coating is preferablyconducted in such a manner that the thickness of the recording layerafter removing the solvent is from 1 to 100 μm.

[0105] In order to record an object to be recorded as a hologram ontothe hologram recording medium according to the present invention,general recording methods can be used. Namely, light having a wavelengthof 200 to 800 nm is split into two, one beam (reference light) andreflected light (object light) obtained from the object to be recordedby irradiating the object with the other beam (or transmitted light(object light) obtained from a volume phase-type master hologram onwhich information of the object is recorded previously by irradiatingthe master hologram with the other beam) are made enter from the sameface or a front face and a rear face of the recording mediumrespectively, and they are made interfere. The hologram recordingmaterial medium is located at a position where an interference fringethus obtained can be caught, and the object is recorded on the medium.

[0106] In more detail, laser light is split into two beams with a beamsplitter or the like, and these beams are mixed again using a mirror orthe like to obtain the interference fringe (two light flux exposuremethod). Alternatively, one laser light is reflected with a mirror, andincident light and reflected light are mixed again to obtain theinterference fringe (one light flux exposure method). When aninterference pattern is obtained, a hologram prepared separately can belocated in a light path as the master hologram, and the interferencefringe can be obtained by the one light flux and/or two light fluxexposure method. The recording medium is located at a position whereintensity distribution of light and shade of the interference patternthus formed can be caught. Irradiating laser light for about fromseveral seconds to several minutes under such an arrangement, aninterference fringe to be a hologram is recorded on the recordingmedium.

[0107] The light amount of the laser light used is, in terms of aproduct of the light intensity and the irradiation time, preferablyabout from 1 to 10,000 mJ/cm². When the light amount is less than therange, recording is difficult to conduct, whereas when it exceeds therange, the diffraction efficiency of the hologram tends to be lowered,and therefore the both cases are not preferred. Light sources to be usedin the present invention can be any light sources which bring aboutpolymerization of the radical polymerizable compound (B) accompanied byelectron transfer when a photo-polymerization initiation systemcomprising the photo-polymerization initiator (D) or a combination ofthe photo-polymerization initiator and the photosensitizing dye isirradiated with light generated from the light source. Typical examplesof light sources are a high-pressure mercury lamp, an ultrahigh pressuremercury lamp, a low-pressure mercury lamp, a xenon lamp and a metalhalide lamp. These light sources can be used when information of themaster hologram is copied into the recording medium or the like. Theselight sources can be used also as light sources when the hologram onwhich the interference fringe is recorded is fixed. A laser can be usedas a preferred light source. Since the laser has a single wavelength andcoherence, the laser is a preferred light source in hologram recording.A more preferred light source is one which is excellent in coherence,for example the laser equipped with optics such as etalon or the like,and has a frequency of the single wavelength adjusted to a singlefrequency. Typical lasers have an oscillating wavelength of 200 to 800nm, and specific examples thereof are Kr laser (wavelength: 647 nm),He—Ne laser (wavelength: 633 nm), Ar laser (wavelength: 514.5 and 488nm), YAG laser (wavelength: 532 nm) and He—Cd laser (wavelength: 442nm). These light sources can be used solely or in combination. The lightsources can be continuous light, or pulse oscillation of the lightsources can be performed at constant or optional intervals. Therecording material can be irradiated with light obtained from the lightsources before or after recording besides in recording.

[0108] After forming the hologram, a post-processing, such asdevelopment and fixing, is not always necessary, but in order tostabilize the resulting image, the medium can be subjected to airradiation treatment with light on the whole surface thereof or a heattreatment to post-polymerize the remaining unreacted monomer.

[0109] In the recording material composition of the invention, thethermoplastic resin (A), the radical polymerizable compound (B), theplasticizer (C) and the photo-polymerization initiator (D) arecompletely dissolved each other before exposure to light, and onirradiation with laser light, the radical polymerizable compound (B) ispolymerized through photo-polymerization, and finally becomes a hologramrecording layer.

[0110] Accordingly, when the two-layer structure, which comprises asubstrate having the recording material composition coated thereon, orthe three-layer structure, which comprises the two-layer structurehaving a protective layer formed on the recording layer, is exposed toan interference fringe having intensity distribution of light and shade,photo-polymerization of the radical polymerizable compound (B) having ahigh photo-polymerization reactivity begins to occur at a portion of alarge light amount, and volume shrinkage occurs at that portion. Anunreacted compound flows from a portion of a small light amount into aconcave portion formed by the volume shrinkage, and the thermoplasticresin (A) diffuses into the portion of a small light amount by phaseseparation between the thermoplastic resin (A) and the radicalpolymerizable compound (B). The radical polymerizable compound (B) isdiffused to migrate into the portion of a large light amount to furtherproceed the photo-polymerization. As a result, a structure wherein thepolymer of the radical polymerizable compound (B) having a highrefractive index is accumulated in the portion of a large light amount,the thermoplastic resin (A) having a low refractive index is accumulatedin the portion of a small light amount is formed.

[0111] The plasticizer (C) is a component to adjust viscosity andcompatibility of the system and functions as a component to promote theseparation between the thermoplastic resin (A) and the radicalpolymerizable compound (B). This agent exists uniformly in the system inthe early stage of the exposure to light but is finally excluded intothe portion of a small light amount, namely to the thermoplastic resin(A) side. Accordingly, a compositional distribution corresponding to anamount of light, i.e., the interference fringe due to a difference inrefractive index between a portion having large amounts of thethermoplastic resin (A) and the plasticizer (C) and a portion having alarge amount of the radical polymerizable compound (B) is formed as ahologram.

[0112] The object to be recorded can be recorded and reproduced by usingthe volume phase-type hologram recording medium according to the presentinvention. Since a usual photograph can record only information ofamplitude of an object, the object recorded on the photograph can beseen only as two dimensions. On the other hand, since the recordingmedium can record information of a phase and amplitude of an object atthe same time, namely can record completely three dimensionalinformation, the recorded object can also be seen as completely threedimensions. Records by the two light flux exposure method are describedin Examples of the present invention, and the object to be recorded ismirror surface in this case. The object light and the reference lightcan be made enter from the same face or the front face and the rear faceon the recording face of the recording medium, and they can be madeinterfere in order to obtain the interference fringe. A transmissiontype hologram is recorded in the former case, and a reflection typehologram is recorded in the latter case. The mirror surface is an objectto be recorded also in the one light flux exposure method, but anotherobject to be recorded is used instead of the mirror, light havingcoherence such as laser light is used as the light source, the recordingmedium is located at a position where the interference fringe formed byinterference between incident light (reference light) and reflectedlight from the object or transmitted light (object light) can be caught,and the object can be recorded on the medium. When the records arereproduced, white light and the light source to be used in recording canbe used as the reference light, and preferably the object light isefficiently reproduced by irradiating the latter light source at thesame angle as that of the reference light in recording the hologram. Avolume phase-type hologram on which the information of the object isrecorded previously can be used in order to obtain the object light. Inthis method, the recorded hologram is used as the master hologram, andthe information of the hologram can be copied by the one light fluxexposure method. In this case, it is possible to record the interferencefringe formed by interference between the reference light (transmittedlight (containing no information of the object) from the masterhologram) and the object light (transmitted light (containing theinformation of the object) diffracted from the master hologram) by theone light flux exposure method. This method has the advantage that it iseasy to perform mass production. Diffraction efficiency evaluated inExamples of the present invention is a proportion(%) of intensity of theobject light to intensity of the reference light, and the formerexpresses brightness of the reproduced light in mirror surface. That is,the diffraction efficiency is an index showing how brightly the objectcan be recorded and reproduced.

BRIEF DESCRIPTION OF DRAWINGS

[0113]FIG. 1 is a schematic drawing showing an example of a transmissiontype hologram.

[0114]FIG. 2 is a schematic drawing showing an example of a reflectiontype hologram.

BEST MODE FOR CARRYING OUT THE INVENTION

[0115] The invention will be specifically described with reference toseveral examples, but the invention is not construed as being limitedthereto.

EXAMPLE 1

[0116] 1) Polyvinyl acetate (“vinyl acetate polymer methanol solution”produced by Wako Pure Chemical Co., Ltd., degree of polymerization:1,400 to 1,600, refractive index of polymer: 1.46) was heated to removemethanol. 4.2 g of the remaining polymer as a thermoplastic resin (A),1.6 g of an acrylic acid adduct of 9,9-bis(4-hydroxyphenyl)fluoreneglycidyl ether (“ASF400” produced by Nippon Steel Chemical Co., Ltd.,refractive index of simple substance: 1.63) as a radical polymerizablecompound (B) having a 9,9-diarylfluorene skeleton and being solid at anordinary temperature and at ordinary pressure, 4.2 g of diethyl sebacate(“SDE” produced by Wako Pure Chemical Co., Ltd., refractive index: 1.43)as a plasticizer (C), 1.5 g of3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone (“BTTB-25”produced by NOF Corporation) as a initiator (D), 0.01 g of acyanine-based dye (“NK1538” produced by Nippon Photosensitizing Dye Co.,Ltd.) as a photosensitizing dye and 11 g of acetone as a solvent weremixed at an ordinary temperature to prepare a recording materialcomposition.

[0117] 2) The composition was coated by a spin coat method on onesurface of a glass plate substrate having a dimension of 60 mm×60 mm toa thickness of 15 to 20 μm after drying. The solvent was removed fromthe coated layer by heat treatment, to produce a recording medium havinga two-layer structure comprising the substrate and the recording layer.

[0118] 3) A PET film having a thickness of 50 μm was placed to cover therecording layer of this recording medium, to produce a three-layerphotosensitive plate for recording a hologram.

[0119] 4) An Ar ion laser of 514.5 nm was split with a beam splitter,angles of each light were changed with a mirror, and both wererecomposed to form interference to obtain an interference fringe. Thephotosensitive plate was placed at a position where this interferencefringe could be caught.

[0120] 5) FIGS. 1 and 2 show examples of a transmission type hologramand a reflection type hologram respectively. In the figures, (A) is alaser emitter, (BS) is a beam splitter, (M) is the mirror, (S) is thephotosensitive plate, (B1) is object light and (B2) is reference light.

[0121] 6) The photosensitive plate was exposed to light under theconditions, and the interference fringe to be the hologram was recordedon the photosensitive plate.

[0122] This exposure to light of the transmission type hologram and thereflection type hologram was carried out using a light intensity on thephotosensitive plate of 1.0 mW/cm² for 0.5 to 100 seconds at an exposedamount of 1 to 200 mJ/cm².

EXAMPLES 2 TO 4

[0123] The amounts of the thermoplastic resin (A), the radicalpolymerizable compound (B) and the plasticizer (C) were changed as shownin Table 1 in the formulation composition in Example 1. The sameoperations as in Example 1 were performed with regard to other points.

EXAMPLES 5 TO 7

[0124] Polymethyl methacrylate (produced by Wako Pure Chemical Co.,Ltd., refractive index of polymer: 1.49), cellulose acetate butyrate(produced by Kanto Chemical Industry Co., Ltd., refractive index ofpolymer: 1.45) and polyvinyl butyrate (“Polyvinyl butyral 1000” producedby Wako Pure Chemical Co., Ltd., refractive index of polymer: 1.45) wereused respectively in the amounts shown in Table 1 instead of polyvinylacetate as the thermoplastic resin (A) in the formulation composition inExample 1. The same operations as in Example 1 were performed withregard to other points.

EXAMPLE 8

[0125] 1) An isobornylmethacrylate monomer (“Light ester IB-X” producedby Kyoeisha Chemical Co., Ltd.) was prepared as cyclic aliphaticmethacrylate obtained by esterification of cyclic aliphatic alcohol withmethacrylic acid, which is one of raw monomers of the thermoplasticresin (A). The isobornylmethacrylate monomer and a methyl methacrylatemonomer (“Light ester M” produced by Kyoeisha Chemical Co., Ltd.) wereadded to two-fold volume of dioxane in a molar ratio of 17:83, theobtained solution was degassed under nitrogen bubbling for two hours,azobisisobutyronitrile was added to the solution as an initiator in anamount of 0.01 mol/l, and a polymerization reaction was performed underreflux at 60° C. The obtained reaction mixture was poured into coldmethanol to precipitate a polymer. The obtained polymer wasreprecipitated twice using tetrahydrofuran as a good solvent andmethanol as a poor solvent to wash it. The obtained copolymer had amolecular weight of 230,000, a glass transition temperature of 158° C.and a refractive index of 1.51.

[0126] 2) 3.7 g of the above-mentioned copolymer as the thermoplasticresin (A), 1.9 g of the acrylic acid adduct of9,9-bis(4-hydroxyphenyl)fluorene glycidyl ether as the radicalpolymerizable compound (B), 4.4 g of diethyl sebacate as the plasticizer(C), 0.82 g of2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1-′biimidazole (“B-CIM”produced by Hodogaya Chemical Co., Ltd.) as the photo-polymerizationinitiator (D), 0.01 g of a cyanine-based dye (“NK1538” produced byNippon Photosensitizing Dye Co., Ltd.) as a photosensitizing dye, 0.373g of mercaptobenzoxazole as a chain-transfer agent and 14 g of acetoneas the solvent were mixed at an ordinary temperature to prepare arecording material composition. The same operations as in Example 1 wereperformed with regard to other points.

[0127] A refractive index of the thermoplastic resin (A) is 1.51, arefractive index of the radical polymerizable compound (B) is 1.63, arefractive index of the plasticizer (C) is 1.43, and a weight ratio ofthe thermoplastic resin (A) to the plasticizer (C) is 3.7:4.4.Accordingly, a weighted mean of the refractive index of thethermoplastic resin (A) and the refractive index of the plasticizer (C)is 1.47. The refractive index of the radical polymerizable compound (B)is larger than the weighted mean of the refractive index of thethermoplastic resin (A) and the refractive index of the plasticizer (C),and its difference is 0.2.

EXAMPLE 9

[0128] The molar ratio of the isobornylmethacrylate monomer to themethyl methacrylate monomer was changed into 25:75 in the step 1) ofExample 8. The same operations as in Example 1 were performed withregard to other points.

[0129] A refractive index of the thermoplastic resin (A) is 1.50, and aweighted mean of the refractive index of the thermoplastic resin (A) andthe refractive index of the plasticizer (C) is 1.46. The refractiveindex of the radical polymerizable compound (B) is larger than theweighted mean of the refractive index of the thermoplastic resin (A) andthe refractive index of the plasticizer (C), and its difference is 0.17.

EXAMPLE 10

[0130] The amount of the copolymer as the thermoplastic resin (A) waschanged into 3.3 g, and the amount of the radical polymerizable compound(B) was changed into 2.3 g respectively in the composition of Example 8.The same operations as in Example 1 were performed with regard to otherpoints.

[0131] Since the weight ratio of the thermoplastic resin (A) to theplasticizer (C) is 3.3:4.4, the weighted mean of the refractive index ofthe thermoplastic resin (A) and the refractive index of the plasticizer(C) is 1.46. The refractive index of the radical polymerizable compound(B) is larger than the weighted mean of the refractive index of thethermoplastic resin (A) and the refractive index of the plasticizer (C),and its difference is 0.17.

EXAMPLES 11 to 13

[0132] 9,9 -Bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene(“bisphenoxyethanolfluorene dimethacrylate, BPEF-MA” produced by OsakaGas Co., Ltd., refractive index of simple substance: 1.625) as theradical polymerizable compound (B), diethyl adipate (ADE, refractiveindex: 1.42) and 2-ethoxyethyl acetate (refractive index of simplesubstance: 1.40) as the plasticizers (C),2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole (“B-CIM”produced by Hodogaya Chemical Co., Ltd.) as the initiator (D) andmercaptobenzoxazole as the chain-transfer agent were used respectivelyin the amounts shown in Table 1. The same operations as in Example 1were performed with regard to other points.

COMPARATIVE EXAMPLES 1 AND 2

[0133] Radical polymerizable compounds (radical polymerizable compounds(B′)) other than the radical polymerizable compound (B) were used in theformulation composition of Example 1. As the radical polymerizablecompounds (B′), 2-phenoxyethyl acrylate (FA) (Comparative Example 1),which is a radical polymerizable compound having no 9,9-diarylfluoreneskeleton and being liquid at an ordinary temperature, and9,9-bis(3-ethyl-4-acryloxydiethoxyphenyl)fluorene (BPF, refractive indexof simple substance: 1.59) (Comparative Example 2), which is a radicalpolymerizable compound having the 9,9-diarylfluorene skeleton and beingliquid at an ordinary temperature, were used respectively in the amountsshown in Table 2. The same operations as in Example 1 were performedwith regard to other points. Thus, when the compound which has the9,9-diarylfluorene skeleton and at least one radical polymerizableunsaturated double bond and is solid at an ordinary temperature and atordinary pressure is not used as the radical polymerizable compound, therefractive index of the radical polymerizable compound is larger thanthe weighted mean of the refractive index of the thermoplastic resin (A)and the refractive index of the plasticizer (C), but sufficientdiffraction efficiency was not obtained as shown in Table 2.

COMPARATIVE EXAMPLES 3 TO 8

[0134] As shown in Table 2, the thermoplastic resin (A), the radicalpolymerizable compound (B) and the plasticizer (C) were blended inratios outside the range defined in the present invention. The sameoperations as in Example 1 were performed with regard to other points.As shown in Table 2, a difference in refractive index of the radicalpolymerizable compound (B) is larger than the weighted mean of therefractive index of the thermoplastic resin (A) and the refractive indexof the plasticizer (C) in these formulations. However, since any one ortwo component(s) exist(s) in too small or large amount(s), sufficientmaterial transfer does not occur in recording holograms and/or fixingafter recording is insufficient. Accordingly, the holograms cannot berecorded, or diffraction efficiency dropped remarkably.

COMPARATIVE EXAMPLE 9

[0135] As shown in Table 2, polypentabromophenyl methacrylate(refractive index: 1.71) as the thermoplastic resin (A),9,9-bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene(“bisphenoxyethanolfluorene dimethacrylate, BPEF-MA” produced by OsakaGas Co., Ltd., refractive index of simple substance: 1.625), which hasthe 9,9-diarylfluorene skeleton and at least one radical polymerizableunsaturated double bond and is solid at an ordinary temperature and atordinary pressure, as the radical polymerizable compound (B) and2-ethoxyethyl acetate (refractive index of simple substance: 1.40) asthe plasticizer (C) were used. The same operations as in Example 1 wereperformed with regard to other points. Thus, each component and eachamount are in the ranges defined in the present invention. However,since a difference in refractive index of the radical polymerizablecompound (B) is smaller than the weighted mean of the refractive indexof the thermoplastic resin (A) and the refractive index of theplasticizer (C), and there is no sufficient difference in refractiveindex, diffraction efficiency dropped remarkably.

COMPARATIVE EXAMPLE 10

[0136] The photosensitive plate for recording prepared in Example 1 wasirradiated with an Ar ion laser of 514.5 nm, a high-pressure mercurylamp (“UM-102”, produced by Ushio Electric Co., Ltd.), an ultrahighpressure mercury lamp (“USH-102D”, produced by Ushio Electric Co.,Ltd.), a xenon lamp (“UXL-500D-0”, produced by Ushio Electric Co., Ltd.)or a metal halide lamp (“UVL-4000M3”, produced by Ushio Electric Co.,Ltd.) as a light source. A method of recording was neither two lightflux exposure nor one light flux exposure, and the photosensitive platefor recording was only irradiated with light. Transmission type andreflection type holograms could not be recorded at all in theseexperiments. Namely, even if a hologram is tried to record using laserlight or light containing ultraviolet radiation (the above-mentionedhigh-pressure mercury lamp or the like), the hologram cannot be recordedunless light is made interfere.

COMPARATIVE EXAMPLE 11

[0137] Two light flux exposure and one light flux exposure wereperformed on the photosensitive plates for recording prepared in Example1 using the high-pressure mercury lamp (“UM-102”, produced by UshioElectric Co., Ltd.), the ultrahigh pressure mercury lamp (“USH-102D”,produced by Ushio Electric Co., Ltd.), the xenon lamp (“UXL-500D-0”,produced by Ushio Electric Co., Ltd.) or the metal halide lamp(“UVL-4000M3”, produced by Ushio Electric Co., Ltd.) instead of the Arion laser of 514.5 nm as the light source. An object to be recorded is amirror in all cases. Transmission type and reflection type hologramscould not be recorded at all in these experiments. Namely, even if lightcontaining ultraviolet radiation is used and light is made interfere, ahologram cannot be recorded by the two light flux exposure method andthe one light flux exposure method unless coherence of light from thelight source is good.

EXAMPLE 14

[0138] One light flux exposure was performed on the photosensitive platefor recording prepared in Example 1 using the high-pressure mercury lamp(“UM-102”, produced by Ushio Electric Co., Ltd.), the ultrahigh pressuremercury lamp (“USH-102D”, produced by Ushio Electric Co., Ltd.), thexenon lamp (“UXL-500D-0”, produced by Ushio Electric Co., Ltd.) or themetal halide lamp (“UVL-4000M3”, produced by Ushio Electric Co., Ltd.)as the light source. An object to be recorded is a transmission typehologram (diffraction efficiency: 75%, resolution: about 500/mm)prepared separately. The transmission type hologram was glued on thephotosensitive plate for recording and irradiated. In this case, objectlight is light diffracted by the transmission type hologram, andreference light is light penetrating the transmission type hologramwithout being diffracted. The hologram could be recorded, anddiffraction efficiency was high, i.e., 90% or higher in all cases. Thus,recording can be made by copying a master hologram using lightcontaining ultraviolet radiation, too.

Evaluation of Performance

[0139] Each film thickness and diffraction efficiency of each hologramafter recording were measured for the holograms obtained in theabove-mentioned Examples and Comparative Examples.

a) Film Thickness

[0140] The film thickness of each hologram after recording was measuredwith a micrometer.

b) Diffraction Efficiency

[0141] The diffraction efficiency of each transmission type hologram wascalculated by determining a ratio of diffracted light to incident lightwith a light power meter (OPTICAL POWER/ENERGYMETER, MODEL 66XLAproduced by PHOTODYNE Co., Ltd.) by the following equation.

Diffraction efficiency (%)=(diffracted light intensity/incident lightintensity)×100

c) The Diffraction Efficiency of the Reflection Type Hologram wasDetermined by Measuring Transmittance with an UltravioletSpectrophotometer (“V-550” Produced by Nippon Spectroscopy Co., Ltd.).d) Glass Transition Temperature

[0142] Each glass transition temperature of each hologram afterrecording was measured with a dynamic viscoelastic properties measuringdevice.

[0143] Examples 1 to 13 and their evaluation results are summarized inTable 1, and Comparative Examples 1 to 9 and their evaluation resultsare summarized in Table 2. TABLE 1 (g) Example 1 2 3 4 5 6 7 8 9 10 1112 13 Thermoplastic resin (A) Polyvinyl acetate 4.2 2 2.5 6.5 3.4 3.43.4 Polymethyl methacrylate 4.2 Cellulose acetate butyrate 4.2 Polyvinylbutyral 5 Copolymer 3.7 3.7 3.3 (Molar ratio of isobornyl methacrylate(17:83) (25:75) (17:83) to methyl methacrylate) Radical polymerizablecompound (B) ASF400 1.6 5.5 1 1 1.6 1.6 2 1.9 1.9 2.3 BPEF-MA 2.6 2.62.6 Plasticizer (C) Diethyl sebacate 4.2 2.5 6.5 2.5 4.2 4.2 3 4.4 4.44.4 Diethyl adipate 4 4 2-Ethoxyethyl acetate 4 Photopolymerizationinitiator (D) BTTB-25 1.5 1.5 1.5 1.5 1.5 1.5 1.5 B-CIM 0.82 0.82 0.820.89 0.89 0.89 Photosensitizing dye Cyanine-based dye NK-1538 0.01 0.010.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 Cyanine-based dye NK-1420 0.020.02 0.02 Chain-transfer agent Mercaptobenzoxazole 0.373 0.373 0.3730.45 0.45 0.45 Solvent Acetone 11 11 11 11 11 11 11 14 14 14 14 14 14Ethanol 4 Difference in refractive index 0.19 0.18 0.19 0.18 0.17 0.170.18 0.2 0.17 0.17 0.19 0.18 0.17 Film thickness (μm) 17 18 17 16 17 1715 16 17 16 15 16 16 Diffraction efficiency (%) (reflection 94 91 94 9297 96 96 97 96 95 96 94 95 type hologram) Diffraction efficiency (%)(transmission 95 92 98 94 97 99 89 96 95 96 98 96 97 type hologram)Transmittance of hologram after 91 89 90 91 88 87 91 91 91 92 92 92 91recording (%) Glass transition temperature (° C.) 115 123 120 49

[0144] TABLE 2 (g) Comparative Example 1 2 3 4 5 6 7 8 9 Thermoplasticresin (A) Polyvinyl acetate 4.2 4.2 0.5 4.5 4.5 0.5 0.5 9Polypentabromophenyl methacrylate 6 Radical polymerizable compound (B)ASF400 4.5 0.5 5 0.5 9 0.5 BPEF-MA 2 Radical polymerizable compound (B′)FA 1.6 BPF 1.6 Plasticizer (C) Diethyl sebacate 4.2 4.2 5 5 0.5 9 0.50.5 2-Ethoxyethyl acetate 2 Photopolymerization initiator (D) BTTB-251.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Photosensitizing dye Cyanine-baseddye NK-1538 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Chain-transferagent Mercaptobenzoxazole Solvent 11 11 11 11 11 11 11 11 11 AcetoneDifference in refractive index 0.14 0.15 0.2 0.19 0.17 0.2 0.18 0.17−0.01 Film thickness (μm) 18 17 16 16 15 16 14 15 15 Diffractionefficiency (%) (reflection type 67 64 29 26 15 0 8 4 3 hologram)Diffraction efficiency (%) (transmission type 78 70 30 30 22 0 12 7 2hologram) Transmittance of hologram after recording (%) 68 83 81 89 8889 91 90 91

[0145] In the tables,

[0146] ASF400: Acrylic acid adduct of 9,9-bis(4-hydroxyphenyl)fluoreneglycidyl ether (produced by Nippon Steel Chemical Co., Ltd.)

[0147] FA: 2-Phenoxyethyl acrylate

[0148] BPF: 9,9-Bis(3-ethyl-4-acryloxydiethoxyphenyl)fluorene

[0149] BTTB-25: 3,3+,4,4′-Tetra(tert-butylperoxycarbonyl)benzophenone(produced by NOF Corporation)

[0150] BPEF-MA: 9,9-Bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene(produced by Osaka Gas Co., Ltd.)

[0151] B-CIM:2,2′-Bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole(produced by Hodogaya Chemical Co., Ltd.)

[0152] Difference in refractive index: [Refractive index of radicalpolymerizable compound (B)]−[Weighted mean of refractive index ofthermoplastic resin (A) and refractive index of plasticizer (C)]

[0153] Table 1 explicitly shows that all the diffraction efficiency andtransmission of the transmission type holograms and the reflection typeholograms obtained in Examples are high, and the diffraction efficiencyis almost saturated at 30 mJ/cm². The holograms suffered no coloring andhad a high brightness without conducting development and fixing. Thehologram records were formed with only the refractive index modulation,but not unevenness on the recording layer, and highly transparentholograms having substantially no absorption in the visible region wereobtained. Further, when the obtained holograms were heated in an oven at60° to 130° C. for about three minutes to three hours, the diffractionefficiency increased by about 3 to 30% while maintaining hightransparency.

[0154] All the glass transition temperatures of the holograms obtainedin Examples 8 to 10 are 100° C. or higher, and the holograms canwithstand use at high temperatures.

[0155] On the other hand, the diffraction efficiency and transmission ofthe transmission type holograms and the reflection type hologramsobtained in Comparative Examples are lower than those of the hologramshaving approximately equal film thickness in Examples, and thediffraction efficiency did not increase even if the holograms wereirradiated with light of 500 mJ/cm² or more.

Industrial Applicability

[0156] In the present invention, in a composition comprising athermoplastic resin (A) which is soluble in a solvent, a radicalpolymerizable compound (B), a plasticizer (C) and a photopolymerizationinitiator (D), a radical polymerizable compound which is solid at anordinary temperature and at ordinary pressure and has a9,9-diarylfluorene skeleton and at least one radical polymerizableunsaturated double bond is used, and each component is selected so thata refractive index of the radical polymerizable compound (B) is largerthan a weighted mean of that of the thermoplastic resin (A) and that ofthe plasticizer (C). Accordingly, a hologram which can record an imagewith high transparency and at high diffraction efficiency can beprepared using the hologram recording material composition of thepresent invention. Since the hologram recording material compositionaccording to the present invention is excellent in film forming propertyand in a solid state after forming a film, too, a heat treatment forsolidifying a flowable composition is not necessary. Further, even if aheat treatment for amplifying diffraction efficiency after recording thehologram is not performed, the composition exhibits sufficiently highdiffraction efficiency. Therefore, the composition of the invention cansimplify the film formation operation and post-treatment in producing ahologram recording medium, and thus exhibits good workability.

[0157] Furthermore, the recording material after recording the hologramhas the high transparency. Since the thermoplastic resin (A) and theradical polymerizable compound (B) are present in the form of thepolymer having the sufficient high molecular weight by only one exposureto light, it is free of the problem in that the record becomes uncleardue to the re-diffusion of them. The recording material is alsoexcellent in long-term heat resistance, weather resistance, solventresistance and the like. Therefore, the operation of development orfixing for stabilizing the recorded image is not necessary, and thus thehologram can be recorded by the real-time operation.

[0158] Further, when a copolymer of cyclic aliphatic methacrylate andmethyl methacrylate is used as the thermoplastic resin (A) which issoluble in the solvent, a glass transition temperature of the copolymeris high. Accordingly, a hologram after recording hardly softens under ahigh-temperature environment, too, and a hologram which is moreexcellent in heat resistance can be prepared.

1. A volume phase-type hologram recording material composition to beused for recording intensity distribution of light and shade of aninterference fringe obtained by making light interfere as a change inrefractive index, characterized in that the composition comprises athermoplastic resin (A) which is soluble in an organic solvent, aradical polymerizable compound (B) which is solid at an ordinarytemperature and at ordinary pressure and has a 9,9-diarylfluoreneskeleton and at least one radical polymerizable unsaturated double bond,a plasticizer (C) and a photopolymerization initiator (D), a weightpercentage ratio of the thermoplastic resin (A), the radicalpolymerizable compound (B) and the plasticizer (C), (A):(B):(C) is 10 to80:10 to 80:10 to 80, and a refractive index of the radicalpolymerizable compound (B) is larger than a weighted mean of that of thethermoplastic resin (A) and that of the plasticizer (C).
 2. A hologramrecording material composition as claimed in claim 1, wherein aweight-average molecular weight of the thermoplastic resin (A) is 10,000to 5,000,000.
 3. A hologram recording material composition as claimed inclaim 1 or 2, wherein the thermoplastic resin (A) is selected from thegroup consisting of a homopolymer of a monomer having an ethylenicunsaturated double bond, a copolymer of the monomer and acopolymerizable monomer which can be copolymerized with the monomer, acondensation polymerization product of a diphenol compound and adicarboxylic acid compound, a polymer having a carbonate group in amolecule thereof, a polymer having an —SO₂— group in a molecule thereof,a cellulose derivative and combinations thereof.
 4. A hologram recordingmaterial composition as claimed in claim 3, wherein the thermoplasticresin (A) is selected from the group consisting of polyvinyl acetate,polyvinyl butyrate, polyvinyl formal, polyvinyl carbazole, polyacrylicacid, polymethacrylonitrile, polyacrylonitrile,poly-1,2-dichloroethylene, an ethylene-vinyl acetate copolymer,polymethyl methacrylate, syndiotactic polymethyl methacrylate,poly-α-vinyl naphthalate, polycarbonate, cellulose acetate, cellulosetriacetate, cellulose acetate butyrate, polystyrene,poly-α-methylstyrene, poly-o-methylstyrene, poly-p-methylstyrene,poly-p-phenylstyrene, poly-p-chlorostyrene, poly-2,5-dichlorostyrene,polyarylate, polysulfone, polyethersulfone, a hydrogenatedstyrene-butadiene-styrene copolymer, transparent polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, a copolymer of cyclicaliphatic(meth)acrylate and methyl(meth)acrylate and combinationsthereof.
 5. A hologram recording material composition as claimed inclaim 4, wherein the thermoplastic resin (A) is a copolymer of cyclicaliphatic(meth)acrylate and methyl(meth)acrylate, and a compositionratio of the ester to the acrylate of the copolymer is 5 to 95:95 to 5expressed in a molar ratio.
 6. A hologram recording material compositionas claimed in claim 4 or 5, wherein the cyclic aliphatic(meth)acrylateconstituting the copolymer of cyclic aliphatic(meth)acrylate andmethyl(meth)acrylate is methacrylate represented by the followinggeneral formula [I],

wherein R¹ and R², the same or different, are hydrogen or lower alkyl,“1” is an integer of 0 to 6, “m” is an integer of 2 to 6, “n” is aninteger of 1 to 5 which is smaller than “m”, any hydrogen atom(s) inalkylene chains (CH₂)₁, (CH₂)_(m) and (CH₂)_(n) can be substituted bylower alkyl, two hydrogen atoms linked to different carbon atoms in thealkylene chain (CH₂)_(m) can be substituted by both terminals of anotheralkylene chain having one to eight carbon atoms to form anothercycloalkane ring, any hydrogen atom(s) in the cycloalkane ring can befurther substituted by lower alkyl, one of carbon atoms in the alkylenechain (CH₂)_(n) has hydroxyl, to which (meth)acrylic acid is linked toform an ester linkage, and the broken line ( - - - ) is the esterlinkage thus formed.
 7. A hologram recording material composition asclaimed in claim 6, wherein a cyclic aliphatic moiety of the cyclicaliphatic(meth)acrylate constituting the copolymer of cyclicaliphatic(meth)acrylate and methyl(meth)acrylate has a bornyl skeleton,an isobornyl skeleton or a norbornyl skeleton.
 8. A hologram recordingmaterial composition as claimed in claim 7, wherein the cyclicaliphatic(meth)acrylate constituting the copolymer of cyclicaliphatic(meth)acrylate and methyl(meth)acrylate is one or a combinationselected from the group consisting of bornyl(meth)acrylate,isobornyl(meth)acrylate and norbornyl(meth)acrylate.
 9. A hologramrecording material composition as claimed in any one of claims 1 to 8,wherein the thermoplastic resin (A) has a glass transition temperature(Tg) of 100° C. or higher.
 10. A hologram recording material compositionas claimed in any one of claims 1 to 9, wherein the radicalpolymerizable compound (B) is selected from the group consisting of9,9-bis[4-(3-acryloyloxy-2-hydroxy)propoxyphenyl]fluorene,9,9-bis(4-methacryloyloxyphenyl)fluorene, 9,9-bis(4-acryloyloxyphenyl)fluorene, 9,9-bis[4-(2-methacryloyloxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene,9,9-bis{4-[2-(3-acryloyloxy-2-hydroxy-propoxy)-ethoxy]phenyl}fluorene,9,9-bis[4- (3-acryloyloxy-2-hydroxy)prop oxy-3-methylphenyl]fluorene andcombinations thereof.
 11. A hologram recording medium wherein arecording layer comprising the hologram recording material compositionas claimed in any one of claims 1 to 10 is formed on a substrate.
 12. Aprocess for producing the hologram recording medium as claimed in claim11, wherein a thermoplastic resin (A), a radical polymerizable compound(B), a plasticizer (C) and a photopolymerization initiator (D) aredissolved in an organic solvent, the obtained solution is applied on asubstrate, and then the solvent is volatilized to form a recordinglayer.